This invention relates generally to cooking utensils for use in microwave ovens. It is well known that foods cooked by exposure to microwave energy cannot obtain the brown surfaces or outer crust which are obtainable with conventional thermal cooking. Another limitation of microwave cooking is that foods made from cereal grains such as, for example, cakes and bread products become soggy and/or leathery. These foods will also not attain the relatively uniform texture which is attainable when they are cooked in a conventional thermal oven.
A number of approaches have been utilized to brown foods in a microwave oven by the use of cooking utensils having microwave absorbing materials such as ferrites embedded within a portion of the utensil, or having a layer of ferrites attached to a portion of the utensil. In a conventional manner, the ferrites absorb microwave energy thereby conducting heat through those utensil surfaces upon which the ferrites are attached and into the food extremities in contact with those utensil surfaces. A disadvantage of these approaches is that they only brown food surfaces which are in contact with, or in close proximity to, the ferrite heated cooking utensil surfaces. These approaches therefore cannot brown the top of food surfaces which rise during the baking process such as cakes or breads. For example, U.S. Pat. No. 4,190,757 discloses a disposable pan having a bottom, shallow sides and cover. Microwave absorbing material is shown covering substantially the entire pan perimeter. The pan is designed to encapsulate a prepared food wherein the food top surface touches, or is in close proximity to, the heated pan cover. In another approach, U.S. Pat. No. 4,486,640 discloses a utensil suitable for cooking relatively flat breads such as, for example, corn bread. A utensil substantially shielded from microwave energy includes a removable top, ferrite embedded bottom and metal sidewalls. The ferrite conducts heat into the bottom and up the relatively short sidewalls. Accordingly, the bottom and sides, but not the top, of the bread are browned by heat conducted thereto.
Another problem with the above approaches is that they will not adequately brown a wide variety of cakes and breads requiring relatively deep sidewalls. The thermal mass of the sidewalls is too large to be uniformly heated by conduction from the bottom layer. Increasing the amount of ferrite embedded in the utensil bottom is not a viable solution since the food bottom would then become scorched. Extending the layer of ferrites up the sidewalls is not a viable solution either. If the deep sidewalls, having a relatively large surface area, are coated with ferrite the food body would be over baked.